The second is more natural but the first is OK. The "-ing" (continuous/progressive) form is often used to provide the background to an action.I was sitting in the bath when the phone rang. The phone rang while I was sitting in the bath.

Thank you for the answer.I understand it is better to use 'be (...ing).'And I understand that sometimes normal verbs ( I mean not be-verb) are also used.

What do you say about the following?

Don' talk to me while I am eating lunch. #1It means 'Don't talk to me if you see me eating lunch.'

Don't talk to me while I eat lunch. #2It means: I eat lunch at noon every day. It usually takes me 30 minutes. I do not want anyone to interfere with me eating lunch. ( Let me know a better expression. ) So don't talk to me during my lunch time.

I wonder if I could explain well, sorry.

( Question 1 )I know #1 is correct, but do you accept #2?

And I think #3 While he drinks a cup of offee, I clean our bed room quickly every morning. is better than #4 While he is drinking a cup of coffee, I clean our bed room quickly every morning. because 'his drinking a cup of coffee' is a 'daily custom' ( practice? or routine? which is better? ). I know it is difficult to explain, sorry, but #4 seems strange to me.

( Question 2 )Is #4 really more natural than #3?

( Question 3 )Are the following expressions OK?

#5 While I sleep, I always dream. #6 While I read a book, I don't want anyone to disturb me.#7 While I go out, please let me know if anyone calls me.

I think #5 and #6 are OK, but #6 is wrong. What do you say about these?

Sorry, I made a mistake.I think #5 and #6 are correct, but #7 is wrong.Because 'go out' means an action to get out of the house and does not mean 'being outside.'After 'while' comes a word which contains some period of time.But 'go out' is just an action and does not contain some period of time.What do you say about this?Thank you.

#1 yes#2 yes - if this is seen to be a habit. But #1 would be more usual#3 and #4. Yes but, here, #4 would be more usual#5 and #6 - yes - but it is slightly poetic#7 I agree with your further analysis. This would be unlikely.